Many types of devices such as instruments for medical and other applications operate through a connection to a separate control unit which provides power and control signals, and may also receive data or some other output from the connected device. In some cases there is some degree of interchangeability in the types of devices that may be physically connected to a given control unit. In these cases it is necessary to ensure that the intended device is connected to the control unit for a given application of the system. However, it may be difficult for device operators to distinguish between different devices which may have similar appearance and differ only in technical capability. Also, particularly medical instruments may be limited to a maximum number of uses or a maximum number of uses before some manner of service is required to ensure proper operation of the instrument.
Systems have been developed to assist in identifying a device such as a medical instrument to be connected in a system for operation. For example, U.S. Patent Application Publication No. 2004/0122419 A1 discloses a system particularly for use in recognizing disposable or reusable optical components that may be connected to a radiation source unit, and for maintaining usage information on such optical components. The system disclosed in this publication employs a radio frequency identification (RFID) transponder located with the connectable device to communicate with the unit to which it is connected. However, radio frequency devices such as these are susceptible to electromagnetic interference which can limit the application and effectiveness of the system.
U.S. Pat. No. 4,878,896 to Garrison et al. discloses an identification arrangement for use with a medical infusion system. The system disclosed in this patent employs a series of light sources and light sensors located on an infusion pump. The light sources and light sensors cooperate with elements on a pump-mounted cassette to provide identification information regarding the cassette. The identification arrangement disclosed in Garrison et al. is cumbersome and not suited for use in many applications in which connected device identification is desired.